while stirred with the thermometer. When the temperature has fallen below
the solidifying point of pure phenol (42°), a crystal of phenol is added, the
mass beginning to crystallise and the temperature rising and then remaining
stationary. The highest temperature shown represents the solidifying
point of the product tested.
5. Solubility. — i c.c. of the material, shaken in a graduated cylinder
with 15 c.c. of water, should give a perfectly clear solution if the product is
pure. The more impurities present, the more insoluble matter remains.
Pure carbolic acid has the melting (solidifying) point, 40-42°, and the boiling
point, 183-184°. Products are sold, however, with lower melting points (down
to 32 °), tins resulting from the presence of small quantities of moisture and
This is obtained mainly from the distillation products of tar and is sold
ciude or pure. Crude pyridine (pyridine bases) consists essentially of bases
of the pyridine and quinoline groups, etc., and may contain other aromatic
bases, pyrrole and ammonia. It is a colourless or yellowish liquid of a
penetrating and peculiarly unpleasant odour, readily volatile and inflam-
mable, soluble in water. Pure pyridine is colourless and miscible in all
proportions with water or ether, b.pt. 116-117°, D 0-980. In the crude
state it is used mainly for the denaturation of spirits for industrial purposes.
The following are the tests made :
1. Colour.— The colour is compared with that of a solution containing
2 c.c. of decinormal iodine solution to a litre, using two glass tubes 150 mm.
long and 15 mm. in diameter, closed with glass discs (polarimeter tubes
may be used).
A colorimeter is more practicable (see Mineral Oils).
2. Behaviour towards Cadmium Chloride.— 10 c.c. of a solution
of i c.c. of the pyridine in 100 c.c. of water are shaken vigorously with 5 c.c.
of a solution of fused cadmium chloride (5 grams in 100 of distilled water).
A copious, crystalline precipitate should form, this being then filtered through
a 9 cm. filter-paper (weighing 0-45-0-55 gram), dried for an hour at 50-70°
3. Detection of Ammonia. — Ammonia in pyridine is readily detected
by means of phenolphthalein or litmus paper, on which the pyridine has
Small quantities of ammonia are best tested for by means of Nessler's
reagent (see Potable Waters), 5 c.c. of the latter being added to 10 c.c. of
a i% solution of the pyridine : if no ammonia is present, only a white
precipitate is formed.
4. Distillation. — 100 c.c. are distilled from a flask of glass or, in
industrial practice, of copper of about 200 c.c. capacity and with a
short neck into which is inserted a bulb rectifier of the dimensions shown
in Fig. 39, this being joined to a condenser at least 40 cm. long and fittedn